Astronomy Picture of the Day

   [1]Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                              2025 September 7
   [2]An illustration of planet Earth is shown where the Earth is tan and
   has no water shown on its surface. In the foreground are several small
    blue spheres showing how much water is known to reside on our planet.
          Please see the explanation for more detailed information.

                        All the Water on Planet Earth
         Illustration Credit: Jack Cook, Adam Nieman, [3]Woods Hole
          Oceanographic Institution; Data source: Igor Shiklomanov

   Explanation: How much of planet Earth is made of water? Very little,
   actually. Although [4]oceans of water cover about 70 percent of Earth's
   surface, these oceans are [5]shallow compared to the Earth's radius.
   The [6]featured illustration shows what would happen if all of [7]the
   water on or near the surface of the Earth were bunched up into a
   [8]ball. The radius of this ball would be only about 700 kilometers,
   less than half the radius of the [9]Earth's Moon, but slightly larger
   than Saturn's moon [10]Rhea which, like many moons in our outer
   [11]Solar System, is mostly water ice. The next smallest ball depicts
   all of [12]Earth's liquid fresh water, while the tiniest ball shows the
   volume of all of Earth's [13]fresh-water lakes and [14]rivers. How any
   of this [15]water came to be on [16]the Earth and whether any
   significant amount is trapped far [17]beneath Earth's surface remain
   [18]topics of research.

                     Tomorrow's picture: butterfly webb
     __________________________________________________________________

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    Authors & editors: [30]Robert Nemiroff ([31]MTU) & [32]Jerry Bonnell
                                 ([33]UMCP)
          NASA Official: Amber Straughn [34]Specific rights apply.
            [35]NASA Web Privacy, [36]Accessibility, [37]Notices;
                A service of: [38]ASD at [39]NASA / [40]GSFC,
                         [41]NASA Science Activation
                           & [42]Michigan Tech. U.

References

   1. https://apod.nasa.gov/apod/archivepix.html
   2. https://apod.nasa.gov/apod/image/2509/WaterlessEarth2_woodshole_2520.jpg
   3. https://www.whoi.edu/
   4. https://www.youtube.com/watch?v=moSBExlLu2M
   5. http://www.cliffshade.com/colorado/images/earth_anatomy.gif
   6. https://www.usgs.gov/media/images/how-much-water-there-earth-0
   7. https://www.usgs.gov/media/images/all-earths-water-a-single-sphere
   8. https://i.redd.it/n6ujzlqv19p51.jpg
   9. https://science.nasa.gov/moon/
  10. https://en.wikipedia.org/wiki/Rhea_(moon)
  11. https://science.nasa.gov/solar-system/
  12. https://apod.nasa.gov/apod/ap220206.html
  13. https://apod.nasa.gov/apod/ap181218.html
  14. https://apod.nasa.gov/apod/ap180826.html
  15. https://en.wikipedia.org/wiki/Origin_of_water_on_Earth
  16. https://apod.nasa.gov/apod/ap970316.html
  17. https://ssec.si.edu/stemvisions-blog/there-ocean-below-your-feet
  18. https://arxiv.org/abs/2503.17906
  19. https://apod.nasa.gov/apod/ap250906.html
  20. https://apod.nasa.gov/apod/archivepix.html
  21. https://apod.nasa.gov/apod/lib/apsubmit2015.html
  22. https://apod.nasa.gov/apod/lib/aptree.html
  23. https://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search
  24. https://apod.nasa.gov/apod/calendar/allyears.html
  25. https://apod.com/feed.rss
  26. https://apod.nasa.gov/apod/lib/edlinks.html
  27. https://apod.nasa.gov/apod/lib/about_apod.html
  28. https://asterisk.apod.com/discuss_apod.php?date=250907
  29. https://apod.nasa.gov/apod/ap250908.html
  30. http://www.phy.mtu.edu/faculty/Nemiroff.html
  31. http://www.phy.mtu.edu/
  32. https://antwrp.gsfc.nasa.gov/htmltest/jbonnell/www/bonnell.html
  33. http://www.astro.umd.edu/
  34. https://apod.nasa.gov/apod/lib/about_apod.html#srapply
  35. https://www.nasa.gov/about/highlights/HP_Privacy.html
  36. https://www.nasa.gov/general/accessibility/
  37. https://www.nasa.gov/privacy/
  38. https://astrophysics.gsfc.nasa.gov/
  39. https://www.nasa.gov/
  40. https://www.nasa.gov/centers/goddard/
  41. https://science.nasa.gov/learners
  42. http://www.mtu.edu/